The explosion of digital technology has sparked rapid growth in multimedia applications merging audio, video and text information. One such application, which is fervently pursued by the cable television industry, involves distribution of cable services such as movies on an on-demand basis.
Currently, the most common service for providing on-demand movies to subscribers is known as the "pay-per-view" service. In accordance with this service, a cable television provider repeatedly plays a movie on a specified channel throughout the day. The show times of the movie are predetermined and approximately two hours apart as a movie is normally two hours long. Based on a known schedule, subscribers may order a movie showing by way of telephone requests.
Another technique for offering on-demand movies which embraces a "nearly on-demand" concept is disclosed in: T. Gillette et al., "Method for Providing Video Programming Nearly on Demand," PCT Publication, WO 92/11713, Jul. 9, 1992. In accordance with this technique, a service provider operates multiple channels which play the same movie on a time offset basis. Through one of these channels, a subscriber is able to view the movie from its beginning at any time by waiting for a period no longer than the offset. For example, if five channels are used, the offset may be set to be 24 minutes. Thus, the wait time for the movie on average is appreciably reduced. On the other hand, the total number of channels used per movie is undesirably increased. Like the pay-per-view service, this technique requires subscribers to request by phone a movie showing.
The above two techniques both suffer a number of drawbacks. One such drawback is unduly limiting the subscribers' choice as the subscribers have to view whatever movies the service provider offers. In addition, the subscribers have to view the movies at the times specified by the service provider. As a result, the subscribers generally need to wait for some significant time before a movie starts.
Thus, the prior art services are technically lacking with respect to a "truly" on-demand multimedia service whereby a subscriber is allowed to choose from a large selection of movies and to view the selected movie instantaneously.
The current multimedia technology may rely on the latest network developments in such areas as asynchronous transfer mode (ATM) communications and optical fiber networks to provide high speed transmission facilities. It however is deficient in the design of a multimedia server capable of delivering multimedia information to virtually any number of subscribers at any given time in an interactive manner. For example, in a truly on-demand multimedia movie service, the interactive capability should allow a subscriber to communicate his/her requests for such video cassette recorder (VCR) functions as rewinding, fast-forwarding, pausing, etc. In home shopping a subscriber should be able to enter purchase orders while the home shopping program is on. Thus, a desirable multimedia server, which has not been achieved in prior art, has to afford two-way communications to and from subscribers, and the capability of routing a wide range of application specific requests and acting on such requests promptly.
The desirable multimedia server must also be capable of handling multiple users simultaneously. For example, with the multimedia server, the service for thousands of people simultaneously accessing a feature movie should be no different from that for two people viewing the same news clip. Due to the real-time aspect of multimedia information, it is necessary to minimize delays caused by excessive service requests at any given time. The desirable multimedia server must ensure continuous and synchronized retrieval of multiple data streams at varying data rates. For example, in quality video broadcast, the video must be transmitted at thirty frames per second. Moreover, the desirable multimedia server should also allow random access to any part of a multimedia event, for example, the last quarter of a football game show which may be of particular interest.